The overlap in the dual epidemics of HIV and imprisonment in the U.S. is well-documented with a prevalence of HIV among prison populations more than three times that of the general population. Prisons are widely recognized as an important setting to address the HIV epidemic: testing and treating HIV-infected prisoners and linking those prisoners into community-based HIV care upon their release may both improve their health and reduce their risk of transmission in communities to which prisoners return. This strategy is commonly referred to as Seek, Test, Treat, and Retain (STTR). There are several NIH-sponsored ongoing and completed studies to evaluate components of the STTR strategy for criminal justice populations. Most focus on ways to increase HIV testing among inmates or improve continuity of HIV care from prisons and jails to the community. However, little research has addressed factors influencing entry into and retention in HIV care during imprisonment. This gap in the literature is significant considering that as many as 63% of known HIV-positive (HIV+) prisoners have not attained viral suppression at their time of release. Failure to attain routine HIV care in prison may portend a high likelihood of failure to enter into community HIV care at release, resulting in poor health and a heightened risk of transmission. Recently, a cascade of HIV care has been used to conceptualize HIV care across a continuum that starts with detection of infection and ends in suppression of viral replication. The strength f this popular model is that it provides a snap shot of gaps across progressive stages of HIV care; a limitation is that the cascade does not convey patients longitudinal patterns of care. This cascade has been enumerated to provide community estimates of engagement in care, but the HIV care cascade has not been applied to correctional settings, where opportunities and barriers to detect and treat HIV may be distinct from those in the community. We propose to examine the HIV care cascade and identify barriers and facilitators to entering and maintaining care and achieving viral suppression in a large southern prison system. In the process, we will evaluate the utility of the cascade outcomes in a prison setting. Specifically we plan to estimate the proportion of prisoners across each stage of the prison HIV care cascade. We will then evaluate whether the cross- sectional Cascade metrics provide a reasonable surrogate for longitudinal patterns of care, and we will identify individual- and system-level factors associated with failing to link into and retain prison HIV care. Finally, we will conduct interviews to understand barriers and facilitators to care from the perspectives of HIV+ prisoners and prison HIV care providers. These proposed activities are key steps in designing and evaluating interventions to strengthen the implementation of the STTR model, with the ultimate goal of improving the health of HIV+ prisoners and diminishing their risk of transmission in prison and in the communities to which they return.